(a) Field of the Invention
The invention relates to a method for inhibiting in vivo immune response and to the use of a soluble recombinant human CD40L or a sequence within said soluble recombinant human CD40L containing the active binding site with CD40 for inhibiting an immune response. The invention also relates to a mouse model of human alloimmunization for testing in vivo effects of an immunotherapy or inhibition of a human antibody response.
(b) Description of Prior Art
Platelet alloimmunization occurs as a result of exposure to “foreign” antigens present in pooled random donor platelet concentrates. A consequence of platelet alloimmunization is the development of a state of refractoriness to subsequent random donor platelet transfusion. Up to 50% of patients with acute leukemia, almost 100% of those with aplastic anemia and 10% of patients with solid tumors, develop platelet alloantibodies. The alloantibodies are most often directed against HLA Class I antigens, although in 10–20% of cases they are directed against platelet-specific antigens such as PlA, Bak, Pen. Effective platelet support for such patients is dependent upon provision of compatible platelets selected by HLA matching and/or platelet crossmatching, approaches which are expensive and, in up to one-third of cases, ineffective. A multitude of clinical and experimental studies have indicated that alloimmunization depends upon (or is at least augmented by) the presence of “contaminating” MHC class II bearing antigen presenting cells (APC) in the transfused blood products.
Investigators have attempted to inactivate donor APC by ultraviolet radiation, or have applied leukofiltration to remove the APC from the transfused product. Most studies, including a large US-based multi-centre study (TRAP, Trial to Reduce Alloimmunization to Platelets) have indicated that the frequency of patients that become alloimmunized is decreased when leukofiltered products are used. However, it is important to note that although these studies reduced the incidence of alloimmunization by approximately 50%, many patients still become alloimmunized.
The major co-stimulatory molecule for B cells is the CD40 molecule. This surface membrane protein which is found on B cells as well as some other cells interacts with a molecule on activated Th cells designated as CD40 ligand (CD40L, gp39 or CD154) CD40-CD40L interaction is critical to B cell activation and differentiation. B cells stimulated with anti-CD40 antibodies undergo transmembrane signaling, cell enlargement, and LFA-1-dependent aggregation. When B cells are stimulated via an appropriate stimuli in combination with anti-CD40, these B cells can proliferate or be induced to isotype switch depending upon the first stimulus. Patients with defective CD40L function have X-linked hyper-IgM syndrome characterized in part by low levels of serum IgG, IgA, and IgE. CD40 and CD40L deficient mice have numerous immune defects including the inability to class switch from IgM to IgG1 and the inability to stimulate allogenic T cells in an in vitro mixed lymphocyte reaction (MLR). Injection of animals with anti-CD40L antibody has been shown to inhibit both a primary and secondary antibody response, as well as prevent the occurrence of anti-DNA antibodies and disease pathology in lupus-prone mice. Further, administration of a soluble form of CD40L to human B cell hybridomas can induce apoptosis (U.S. Pat. No. 5,540,926). While the CD40 molecule on the B cell provides co-stimulation to that cell via interaction with a Th cell expressing the CD40L, it is important to note that the T cell also becomes activated by this mutually synergistic interaction.
It would be highly desirable to be provided with a method to inhibit in vivo alloimmunization.